Many communication systems or networks, both wired, e.g., Ethernet, and wireless, e.g., HF, VHF, UHF, radio, utilize a form of Carrier Sense Multiple Access (“CSMA”) to determine whether a frequency or radio channel is being used by another station or stations before using the frequency or channel. However, this technique does not work well in the noise- and interference-rich environment of radio communications. In some systems, a known sequence, i.e., a training sequence, is interspersed in modem waveforms to assist in signal detection and channel tracking.
However, signal detection of standard HF modem waveforms is further hampered by the use of heavily filtered Phase Shift Keyed (“PSK”) waveforms (e.g., M-PSK). These waveforms are extremely noise-like in nature and difficult to distinguish from background noise and interference. Without the presence of the training sequence, the ability to determine the presence or absence of these waveforms is extremely difficult to achieve.
Hence, there is a need in the industry for a system that is able to determine the presence or absence of a PSK signal without the need of a training sequence. Embodiments of the present invention are related to the field of digital communications and more specifically determining whether a communication signal is present or absent to meet the above-identified needs. More specifically, methods and systems for determining the presence or absence of a digital communication signal are disclosed. One method comprises the steps of collecting a plurality of signal samples at a selected frequency for a known period of time, determining a metric dependent upon at least one measured characteristic associated with the collected signal samples, and indicating signal status as present when the determined metric is greater than a known value. In another aspect, the method may indicate the signal status as absent when the determined metric is less than said known value. Other embodiments of the present inventive method may further be used to determine the known value by determining a metric for a plurality of samples for a plurality of signal conditions.
It is to be understood that these drawings are solely for purposes of illustrating the concepts of the invention and are not intended as a definition of the limits of the invention. The embodiments shown in FIGS. 1 through 5 and described in the accompanying detailed description are to be used as illustrative embodiments and should not be construed as the only manner of practicing the invention. Also, the same reference numerals, possibly supplemented with reference characters where appropriate, have been used to identify similar elements.